How do I make a normal/displacement map when all I have is a photo?
I've compiled a list of options when it comes to normal and bump map creation. All that remains is to try few of these out and see which results you like best.

To me, the most advanced of the free solutions is MaPZone 2.6, but I haven't tried any of these so I am not sure.

Or you can try the web based Smart Normal, for very basic normal maps generation.

Another tool is  Knald which offers high quality, accurate height maps generated from a Normal/Derivative or photo-sourced texture.

I didn't include urls, since they can be easily googled.